OBJECTIVES: The purpose of the study was to investigate the perceived influence of stress on psoriasis onset and disease severity in a large sample of psoriatics and to compare stress reactors and non-reactors with respect to psoriasis-related stress, disease severity, family history of psoriasis and sociodemographic factors. PATIENTS/METHODS: A total of 5795 members of the Nordic psoriasis associations and 702 patients recruited from Nordic dermatologists or university clinics were asked whether their first outbreak of psoriasis occurred during times of worry and stress. They were also asked to rate the degree to which their psoriasis was influenced by stress and to complete the Psoriasis Life Stress Index, the Psoriasis Disability Index and a number of additional questions concerning sociodemographic factors. RESULTS: Seventy-one per cent of the members and 66% of the patients reported that their psoriasis was exacerbated by stress, and 35% in both groups reported that the onset of their psoriasis occurred during a time of worry and stress. Stress reactors, scoring above the median on stress reactivity, reported greater disease severity, psoriasis-related stress and impairment of disease-related quality of life. They also reported more frequent use of tobacco, tranquillizers and antidepressants. More women than men were stress reactors, and stress reactors were more likely to have a family history of psoriasis. CONCLUSION: Our findings confirm and extend the results of previous studies and indicate that a subgroup of psoriatics may be more psychologically reactive to their disease and its influence on everyday life. Whether this group is also physiologically more reactive to psychosocial stress remains to be investigated.